There will be a total of 9 study clinic visits conducted on an outpatient basis. Subjects who meet the eligibility criteria at Screening (Visit 1) will complete a 7 to 14 day run-in period followed by a 24-week treatment period. Clinic visits will be at Screening, Randomization (Day 1), Day 2, after 4, 8, 12, 16, and 24-weeks of treatment, and 1 day after the Week 24 Visit (also referred as Treatment Day 169). A follow-up contact for adverse assessment will be conducted by telephone approximately 7 days after Visit 9 or the Early Withdrawal Visit. The total duration of subject participation, including follow-up will be approximately 27 weeks. All subjects will be provided with albuterol/salbutamol for use on an "as-needed" basis throughout the run-in and study treatment periods.